Error detection/correction and fault detection/recovery – Pulse or data error handling – Memory testing
Reexamination Certificate
1998-08-28
2001-05-08
Moise, Emmanuel L. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Memory testing
C235S492000, C324S512000, C324S765010, C365S201000
Reexamination Certificate
active
06230291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a microcomputer and a burn-in test method thereof and more particularly a microcomputer including a burn-in test circuit and a burn-in test method thereof.
2. Description of the Related Art
There has been known a microcomputer which is provided with a testing function by which a test mode for testing its operation can be set from the outside, in addition to the user mode for the use by the user. As the operation test of the microcomputer, a burn-in test by which the initial defects of the microcomputer are checked by operating it under the conditions of application of thermal and electrical stresses is generally employed.
An example of the conventional microcomputer for which the test mode can be set from the outside is shown in FIG.
5
.
A microcomputer
5
is composed of a central processing unit (CPU)
51
, a ROM
52
, a mode decoder
54
, an address bus
56
, a data bus
57
, and a NOR circuit
61
. The ROM
52
is composed of a user ROM
52
a
, a test ROM
52
b
, an address decoder
53
, AND circuits
63
and
64
, and a NOT circuit
62
. The user ROM
52
a
and the test ROM
52
b
respectively have address lines corresponding in numbers to their addresses, and access to them can be gained when the address lines are activated.
The test mode for the microcomputer
5
can be set at either one of ROM dump mode (for a ROM dump mode signal S
1
of “1”), burn-in test mode (for a burn-in test mode signal S
2
of “1”), or test ROM execution mode (for a test ROM execution mode signal S
3
of “1”) according to the mode set signals input to mode set terminals
54
a
to
54
c.
In the burn-in test, since the voltages applied to respective terminals of the microcomputer
5
are determined according to the wiring connection of the burn-in test device on which the microcomputer
5
is mounted, the mode set signals input to the mode set terminals
54
a
to
54
c
of the microcomputer
5
are determined accordingly. It is true that the turn-in test mode signal S
2
and the test ROM execution mode signal S
3
are effectively the same, so that the burn-in test can also be carried out by setting the test ROM execution mode.
In the burn-in test mode, the burn-in test mode signal S
2
alone is set exclusively at “1” (high level) by the mode set signals determined in accordance with the wiring connection of the burn-in test device. In this case, an address signal TAD is supplied to the address lines of the test ROM
52
b
via the NOR circuit
61
, the NOT circuit
62
, and the AND circuit
63
, and the CPU
51
gains access to the test ROM
52
b
according to the address decoded by the address decoder
53
. In this way, the test program in the test ROM
52
b
is executed.
Here, the test program is for operating various parts of the microcomputer
5
. Namely, while letting the CPU
51
execute the test program in the test ROM
52
b
, it lets various sections of the microcomputer
5
operate under the conditions of application of thermal and electrical stresses to perform the burn-in test. After the completion of the burn-in test, the program in the test ROM
52
b
is executed in the test ROM execution mode (where no thermal stress is applied to the microcomputer
5
), and initial defects in the microcomputer
5
are detected by verifying the data output via an external input/output terminal
56
a
of the address bus
56
and an external input/output terminal
57
a
of the data bus
57
.
However, in the conventional microcomputer
5
described above, in the burn-in test mode, access to the user ROM
52
a
is not gained since an address signal UAD is not supplied to the address lines of the user ROM
52
a
. That is, in the burn-in test mode, the user ROM
52
a
is not subjected to an electrical stress. Accordingly, even if a burn-in test is carried out by mounting the microcomputer
5
on the burn-in test device, and storage contents of the user ROM
52
a
is dumped under the condition where the normal thermal stress is not applied, it is not possible to fully detect the initial defects of the user ROM
52
a.
In the meantime, it is conceivable to make the mode set signals input to the mode set terminals
54
a
to
54
c
to serve as signals for the ROM dump mode in order to gain access to the user ROM
52
a
, and carry out the burn-in test of the microcomputer
5
in this state.
However, in this case there is required a burn-in test device for giving a mode set signal in the ROM dump mode, in addition to the burn-in test device for giving a mode set signal in the burn-in test mode. Moreover, it becomes necessary to demount the microcomputer
5
from the burn-in test device after the completion of the execution of the test program in the burn-in test mode, and mount it on a separate burn-in test device, which requires much labor.
As a microcomputer having the conventional burn-in test function one may mention the microcomputer disclosed in Publication of Unexamined Patent Applications No. Hei 4-238543. However, this invention discloses only the execution of a test program at the time of burn-in test, similar to the above, and no method of access to the user program storage area is disclosed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a microcomputer and its burn-in test method which enables one to detect initial defects of sections that need defect detection by means of the burn-in test while mounting the microcomputer on the same burn-in test device.
It is another object of the present invention to provide a microcomputer and its burn-in test method which suppresses the increase in the cost of manufacture of the microcomputer without necessitating separate installation of terminals for the detection of initial defects in sections requiring defect detection in the burn-in test, and makes it possible to carry out a burn-in test using the conventional burn-in test device.
In order to achieve the above objects, the microcomputer according to a first viewpoint of this invention is a microcomputer provided with a user program storage means for storing a user program for service to the use of the user and a test program storage means for storing a test program for carrying out operation test, which has a switch signal input means for inputting, at the time of the burn-in test of the microcomputer, a switching signal capable of switching between access to the user program storage means and access to the test program storage means while mounting the microcomputer on the same burn-in test device, wherein the access to the user program storage means and the access to the test program storage means can be switched in response to the input of the switching signal from the switch signal input means.
It should be noted that what is meant by the burn-in test in the above is an operation test for detecting initial defects under the conditions of application of thermal and electrical stresses to the microcomputer, and in reality, the initial defects of the microcomputer are detected from the data obtained by a normal test which is given following the burn-in test.
Moreover, the user program stored in the user program storage means and the test program stored in the test program storage means include not only programs in their literal sense but also data that are used in the programs.
With this arrangement, it is possible to gain access to both of the user program storage means and the test program storage means in the state where the microcomputer is mounted on the same burn-in test device. In other words, since the burn-in test can be carried out by applying an electrical stress also to the user program storage means access to which is not normally gained in the test program, it is possible to detect the initial defects at all locations which require defect detection.
In order to achieve the above objects, the microcomputer according to a second viewpoint of this invention is a microcomputer possessing a test function, and comprises a user program storage means for storing a user program to ser
McGinn & Gibb PLLC
Moise Emmanuel L.
NEC Corporation
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